Vibrational Raman and infrared spectroscopic transitions are used to probe the dynamical and conformational properties associated with lipid-lipid and lipid-protein interactions in membrane systems. For example, the phase transition characteristics for the members of an homologous series of saturated, symmetrical phosphatidylcholine bilayer dispersions were investigated by Raman spectroscopy for even carbon chain length systems extending from C(10) to C(22). A Raman spectral parameter Delta IR, which represents changes in a specific C-H stretching mode intensity ratio across the gel to liquid crystalline phase transition Tm, is correlated with Delta S, the entropy change at Tm determined by calorimetry.